Online Notes on Chapter = 9 ( Heredity and Evolution) Part 3

This is Online Notes on Chapter = 9 ( Heredity and Evolution)  Part 3 for
preparation of CBSE BOARD Examination, NTSE etc.





Evolution and Classification:

Both evolution and classification are interlinked =>

1. Classification of species is reflection of their evolutionary relationship.
2. The more characteristic two species have in common the more closely
they are related.
3. The more closely they are related, the more recently they have a common
ancestor.
4. Similarities among organisms allow us to group them together and to
     study their characteristic.

TRACING EVOLUTIONARY RELATIONSHIPS:

(Evidences of Evolution)

I. Homologous Organs: (Morphological and anatomical evidences). These
are the organs that have same basic structural plan and origin but different functions.

Homologous organs provides evidence for evolution by telling us that they
are derived from the same ancestor.

Evolution by Stages:

Evolution takes place in stages i.e., bit by bit generations.

I. Fitness Advantage:

Evolution of Eyes : Evolution of complex organs is not sudden. It occurs
due to minor changes in DNA, however takes place bit by bit over generations.

• Flat worm has rudimentary eyes. (Enough to give fitness advantage)
• Insects have compound eyes.
• Humans have binocular eyes.

II. Functional Advantage:
Evolution of Feathers : Feathers provide insulation in cold weather but later
they might become useful for flight.
Example, Dinosaurs had feathers, but could not fly using feathers. Birds
seem to have later adapted the feathers to flight.

Although there is great diversity of human forms all over the world, yet all
humans are a single species.

GENETIC FOOTPRINTS OF HUMANS:

Hundreds/thousand of years ago

• They did not go in a single line.
• They went forward and backward.
• Moved in and out of Africa.
• Sometimes came back to mix with each other.

Genetic Terminology:

1. Gene : Mendel used the term factor for a gene. A gene is the unit of
DNA responsible for the inheritance of character.

2. Allele : A pair of genes that control the two alternatives of the same
character e.g., TT/tt.

3. Heterozygous : The organism in which both the genes of a character are
unlike e.g., Tt.

4. Homozygous : The organism in which both the genes of a character are
similar e.g., TT, tt.

5. Dominant : The gene which expresses itself in F1 generation is known
as dominant gene.

6. Recessive : The gene which is unable to express itself in presence of the
dominant gene.

7. Genotype : It is the genetic constitution of an organism which determines
the characters.

8. Phenotype : It is the appearance of an individual.

9. Micro-evolution : It is the evolution which is on a small scale.

10. Species : A group of similar individuals within a population that can
interbreed and produce fertile offspring.

11. Chromosome : Thread like structures present in the nucleus of a cell,
containing hereditary information of the cell.

12. DNA : Deoxyribose Nucleic Acid.
It is present in chromosomes which carries traits in a coded form, from one
generation to the next.

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